1. Field of the Invention
The present invention relates to an imaging lens array, and more particularly to an aspherical type imaging lens array that comprises, from object side to image side, at least an aperture, a first lens, a second lens and a third lens.
2. Description of the Prior Art
Image sensor has been widely used in different areas nowadays. For example, the mobile phone also has been equipped with such an image sensor comprised of a solid state imaging device and lens, such as Charge Coupled Device (CCD) sensor. With the development of science and technology, the mobile phone is becoming more and more smaller, therefore the lens array in the mobile phone also needs to be miniaturized. To reduce the size of the lens array, the length of it must be shortened, however, this is likely to bring an adverse effect to the telecentric performance of the lens array.
A conventional solution to the telecentric problem of the mini imaging lens array is to arrange an aperture at the object side while arranging the exit pupil at a position far away from the image side. The lens array is usually made up of three plastic aspherical lenses. Below are three examples of conventional mini imaging lens arrays.
JP Published patent application No. 2004-4566 discloses an imaging lens array that comprises, from the object side, an aperture, a first biconvex lens having positive power, a second negative lens whose concave surface facing the object side, and a third meniscus lens whose convex surface facing the object side. Each of the lenses has at least an aspherical surface.
JP Published patent application No. 2004-226487 discloses an imaging lens array comprising, from the object side, a first positive lens with a convex surface facing the object side, an aperture formed either on the object side or the image side of the first positive lens, a second meniscus lens with a concave surface facing the object side, and a third meniscus lens with a convex surface facing the object side. The first and the second lenses each have at least an aspherical surface, and both side of the third lens are aspherical.
JP Published patent application No. 2004-240063 discloses an imaging lens array comprising, from the object side, a first positive lens with a convex surface facing the object side, a second meniscus lens with a concave surface facing the object side, and a third positive lens with a convex surface facing the object side.
However, the abovementioned lens arrays still have some shortcomings. For example, the magnification of the imaging lens array of JP Published patent application No. 2004-4566 is as high as 1.3–1.55, and when the magnification is 1.3, its corresponding Fno value will be 4.15. In this condition, the imaging lens array is unable to provide enough brightness. The magnification of the imaging lens array of JP Pt 2004-226487 is 1.44–1.88, and that of the imaging lens array of JP Pt 2004-240063 is also as high as 1.42–1.56.
By the way, the magnification (T/f) is the ratio of the focal length (f) to the entire optical length (T). The entire optical length T is the distance between the object side of the first lens and the image side.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.